1. Field of the Invention
The present invention relates to a structure of a bearing that holds a rotary body. The invention more particularly relates to a journal bearing that prevents seizure and holds a rotary body with a high load, and to a lubricant supply structure of the journal bearing, which is designed to supply a cooled lubricant to a back surface of the bearing and reduce the temperature of the bearing.
2. Description of the Related Art
An elliptical bearing has been generally used to prevent a self-excited oscillation as a bearing holding a large rotary body (e.g., for a thermal power plant) in which a natural frequency of a multi-span shaft is relatively low.
Since a primary critical speed of a bearing for a steam turbine having a large capacity, like a conventional steam turbine shown in FIG. 17, is low, an oil groove is provided at a central portion of a lower bearing 2a in the direction of the width of the lower bearing 2a and extends along a circumferential direction of the lower bearing 2a to reduce load capacity of the bearing, increase an eccentricity ratio, and ensure stability. Because a rim speed of such a large-scaled bearing is approximately 100 m/s, flow of a lubricant is turbulent, and apparent viscosity of the lubricant increases. Thus the temperature of the bearing tends to increase. Therefore, a cooling groove is provided in an upper half bearing 2b. The cooling groove is designed to cool the rotary shaft, and it is therefore difficult to cool the highest-temperature portion of the bearing.
JP-A-H08-93769 discloses a technique for cooling a bearing. As disclosed in JP-A-H08-93769, a circumferential oil groove and a dam are provided in a shaft-sliding surface of the bearing, and pressure of a lubricant agent present in the dam is adjusted, to prevent the bearing from burning and a rotary shaft from unstably shaking.
JP-A-H10-213130 and JP-A-2006-138353 disclose that a groove is provided in a back metal, and a lubricant is supplied to the groove to cool the back metal. This prevents a bearing from burning. In addition, JP-A-2004-92878 discloses that a hydrostatic bearing has a cooling medium supply pocket formed in an outer circumferential surface thereof. A cooling medium or a lubricant is supplied to cool the bearing.